The crudest form of a prosthesis is a hard, stump-receiving socket. If a socket is for receiving the stump of a below-the knee amputee, it will be attached by suitable means to a prosthetic foot; if it is for an above-the knee amputee, it will be attached to a prosthetic knee as well. In either application, the amputee will experience discomfort arising from contact between the stump and the hard interior of the stump-receiving socket unless an adequate cushioning means is provided. Moreover, the socket will separate from the stump unless an attachment means is provided.
Some prosthetic devices are held onto the residual limb (amputation stump) by suction. When the residual limb is fully inserted, usually with the aid of a sock, the tissue is pulled slightly downwardly, by pulling on the sock, and this creates a suction within the socket that holds it on. Obviously, this suction must be maintained if the socket is to remain in place; this is accomplished by a check valve. It is equally obvious that a socket equipped with a check valve is more expensive than a socket without such a valve.
Another socket attachment method intended to make the downward pulling on the tissue easier includes the use of a cream-like material. A predetermined quantity of the cream is applied to the residual limb and said residual limb is then inserted into the socket. Although this method works, it is messy; the cream often soils the amputee's clothing, for example.
Some individuals fit socks over their residual limb in an attempt to make the prosthesis more comfortable. Several layers of socks will form a reasonably soft cushion, but there are a number of drawbacks to the use of socks as socket liners. Perhaps the most obvious limitation is the inability of socks to protect a particular point or area where extra cushioning is needed, i.e., socks provide the same amount of cushioning everywhere. Moreover, the diameter of a stump will vary during the day, especially where the amputee is active. Specifically, most stumps shrink in size as the day progresses because walking and other activities drives fluids out of the stump; this results in the need for more layers of socks and that need requires the amputee to travel throughout the day with a supply of extra socks on hand. It is also troublesome and time-consuming to remove the socket, add a layer or two of socks, and to reattach the socket several times per day. Amputees who use socks as cushioning means are of course familiar with other drawbacks not mentioned herein.
Perhaps even more problematic than daily stump volume variations are the long term variations brought about by long term weight loss or weight gain.
In response to the limitations of socks as a means for cushioning, inventors have developed a number of alternatives thereto. Perhaps the simplest, most obvious alternative is to line the socket with a cushioning means. The problem with cushioned stump-receiving sockets is equally obvious, i.e., the fit between the socket and the stump becomes loose as the day progresses, and the amputee must again resort to the expedient of employing multiple layers of socks to maintain a reasonably tight fit as required.
Cushioned sockets, like socks, also fail to provide extra cushioning to particular points or areas.
Accordingly, customized cushioning means have been developed so that each individual amputee may have a cushioning means that matches the contour of his or her residual limb. A cast is made of the stump by wrapping plaster bandages around it, or by simply inserting the stump into a vat of impressionable material. The negative of the stump thereby created is then filled with plaster or other suitable material; this produces a replica of the residual limb. A liner is then fabricated that provides the proper amount of cushioning at the places where extra cushioning is needed.
Although liners so fabricated are superior in performance to socks and non-customized liners, they do not compensate for the changes in size of the stump during a day or from day to day. Moreover, such liners are expensive because they must be made for one patient at a time.
In an attempt to provide customized liners that compensate for changes in stump size, inventors have developed liners that include inflatable bladders. Thus, as the day progresses, more air is introduced into preselected bladders to maintain the tight fit between the socket and stump and to maintain the amputee's comfort level.
Even these advanced liners have shortcomings. Their primary drawback is that they must be customized with a high degree of precision for each patient. Thus, they cannot be mass produced and their unit cost is therefore quite high.
For example, in U.S. Pat. No. 4,923,475 to Gosthnian et. al., the stump-engaging surface of each bladder is molded to have a shape conforming to the outer surface of the amputee's stump when the stump is under static pressure, i.e., the patient stands to place static pressure on the stump, and the bladders are made so that they conform, when deflated, to the particular contour of the stump thereby produced. This highly exacting procedure does not lend itself to mass production.
U.S. Pat. No. 4,923,474 to Klasson et. al. eschews bladders and discloses a liner that has a distal end that is highly elastic in a radial direction so that it tightly and snugly engages the stump as the stump changes size, yet which is substantially inelastic axially so that it will not stretch with the weight of a prosthesis.
In summary, even though the art of prosthetics is old and well-developed, it is still unsatisfactory in several major respects. Specifically, the art has failed to produce a highly effective yet simple means for providing a suction that prevents inadvertent separation of limb and socket, and it has failed to produce a cushioning means that can be easily adapted to fit an individual. Significantly, at the time the present invention was made, the art neither taught nor suggested to those of ordinary skill how the limitations of the prior art devices could be overcome.